Determination of the stress-strain state of structures made of viscoelastic fibrous composite materials based on the stiffness matrix of a spatio-temporal finite element

Abstract

Abstract. Increase in spheres of composite materials application leads to the need to improve the methods of composite structures calculation, increase their efficiency and adequacy to real processes. The use of fibrous composite materials creates difficulties in determining the stress-strain state of the structure due to the different physical and mechanical properties of the material components. As a rule, a fibrous composite consists of two components: a matrix and a fiber. The matrix ensures the material monolithicity fixing the shape of the product and the relative position of the reinforcing fibers. The fibers absorb the main stresses that occur during operation, and provide rigidity and strength of the composite. The combination of the matrix and fiber properties allows creating special types of composites to be used in various equipment. The use of rubber as a matrix gives the structure viscoelastic properties, which can be seen in the deformation creeping and stress relaxation in the material, which complicates the calculation of the stress-strain state of the whole structure greatly. The paper proposes an approach that is the development of a moment scheme of finite elements in the form of the displacements method based on the Lagrange principle. Using this approach, a special space-time finite element has been developed that takes into account the viscoelastic properties of the material matrix and the fiber elastic properties. The proposed numerical approach allows obtaining a solution to the problems of viscoelasticity of composite materials mechanics in three-dimensional model. Using the applications package created on the basis of this approach, the calculation of the stress-strain state of a single-cavity pneumatic cylinder with a rubber cord shell has been done. The influence of the reinforcement scheme and rubber viscoelastic properties on the parameters of the pneumatic cylinder deformation has been analyzed. In particular, it becomes possible to adjust the structure stiffness properties by changing the orientation, type and concentration of fibers, as well as the type of matrix and other material characteristics. Keywords: fibrous composite material, viscoelasticity, space-time finite element.